1. Field of the Invention
The present invention relates to an imaging apparatus with an exposure controlling mechanism, in particular relating to an imaging apparatus realizing the driving of a plurality of iris blades so as to differ in amounts and phases of their displacements from each other by means of a single driving motor.
2. Description of the Related Art
In an exposure controlling mechanism of an imaging apparatus such as a video camera, there has come to be used an imaging apparatus changed to be small in size, light in weight and cheap in cost by using two iris blades moving in opposite directions to each other on a line in place of the so-called iris diaphragm which adjusts the diameter of an aperture of a diaphragm by rotating a plurality of iris blades around an optical axis.
However, if the diameter of the aperture becomes too small much when an object is bright, the degradation of the picture quality owing to diffraction, the coming out of dust owing to the increase of the depth of focus, and so forth become problems.
Accordingly, there comes an imaging apparatus which prevents an extreme small diaphragm aperture state by affixing an ND (neutral density) filter on one of the iris blades and protruding the ND filter into a cutoff of the iris blade for forming the iris aperture.
FIG. 5 shows an exposure controlling mechanism xe2x80x9caxe2x80x9d having the structure mentioned above. The exposure controlling mechanism xe2x80x9caxe2x80x9d comprises two iris blades xe2x80x9cbxe2x80x9d and xe2x80x9ccxe2x80x9d and a driving means xe2x80x9cdxe2x80x9d for driving these iris blades xe2x80x9cbxe2x80x9d and xe2x80x9ccxe2x80x9d.
In one iris blade xe2x80x9cbxe2x80x9d, a cutoff xe2x80x9cexe2x80x9d for forming an iris aperture is formed at the lower edge thereof. Moreover, at positions near to the right side edge and the left side edge of the iris blade xe2x80x9cbxe2x80x9d, two guided slits xe2x80x9cfxe2x80x9d extending in the vertical direction and a guided slit xe2x80x9cgxe2x80x9d extending also in the vertical direction are formed, respectively. Furthermore, an elongated link aperture xe2x80x9chxe2x80x9d extending in the horizontal direction is formed at a position right above the guided slit xe2x80x9cfxe2x80x9d on the upper right side.
Then, guide pins provided to a housing, not shown, having a light penetration aperture are slidably engaged with the guided slits xe2x80x9cfxe2x80x9d and xe2x80x9cgxe2x80x9d, respectively. Thereby, the iris blade xe2x80x9cbxe2x80x9d is supported by the housing slidably in the vertical direction.
In the other iris blade xe2x80x9ccxe2x80x9d, a cutoff xe2x80x9cixe2x80x9d for forming an iris aperture is formed at the upper edge thereof. An ND filter xe2x80x9cjxe2x80x9d is attached to the blade xe2x80x9ccxe2x80x9d so as to cover the lower end portion of the cut off xe2x80x9cixe2x80x9d for forming the iris aperture. Moreover, at positions near to the left side edge and the right side edge of the iris blade xe2x80x9ccxe2x80x9d, two guided slits xe2x80x9ckxe2x80x9d extending in the vertical direction and a guided slit xe2x80x9clxe2x80x9d extending also in the vertical direction are formed, respectively. Incidentally, an ND filter having a transmission factor of, for example, 10 percent is used as the ND filer xe2x80x9cjxe2x80x9d. Furthermore, an elongated link aperture xe2x80x9cmxe2x80x9d extending in the horizontal direction is formed at a position right above the guided slit xe2x80x9ckxe2x80x9d on the upper left side.
Then, similarly to the iris blade xe2x80x9cbxe2x80x9d, guide pins provided to the housing, not shown, are slidably engaged with the guide slits xe2x80x9ckxe2x80x9d and xe2x80x9clxe2x80x9d, respectively. Thereby, the iris blade xe2x80x9ccxe2x80x9d is supported by the housing slidably in the vertical direction.
The driving means xe2x80x9cdxe2x80x9d comprises a driving motor xe2x80x9cnxe2x80x9d attached at an upper part of the riot shown housing and an operation arm xe2x80x9coxe2x80x9d fixed to a rotation axis of the driving motor xe2x80x9cnxe2x80x9d. The operation arm xe2x80x9coxe2x80x9d is formed to be elongated horizontally, and a center portion of the operation arm xe2x80x9coxe2x80x9d is fixed to the rotation axis of the driving motor xe2x80x9cnxe2x80x9d. A connecting pin xe2x80x9cpxe2x80x9d is projectingly fixed at each end on the right side and the left side of the operation arm xe2x80x9coxe2x80x9d. Then, the connecting pin xe2x80x9cpxe2x80x9d on the right side is slidably engaged with the elongated link aperture xe2x80x9chxe2x80x9d of the iris blade xe2x80x9cbxe2x80x9d, and the connecting pin xe2x80x9cpxe2x80x9d on the left side is slidably engaged with the elongated link aperture xe2x80x9cmxe2x80x9d of the iris blade xe2x80x9ccxe2x80x9d.
Consequently, because the connecting pins xe2x80x9cpxe2x80x9d move in opposite directions from each other, respectively, when the operation arm xe2x80x9coxe2x80x9d is rotated in conformity with the operation of the driving motor xe2x80x9cnxe2x80x9d, the iris blades xe2x80x9cbxe2x80x9d and xe2x80x9ccxe2x80x9d that are linked to those connecting pins xe2x80x9cpxe2x80x9d respectively move to the upper direction and the lower direction oppositely. This changes the iris aperture (diaphragm aperture diameter) regulated by the respective cutoffs xe2x80x9cexe2x80x9d and xe2x80x9cixe2x80x9d for forming the iris aperture of the iris blades xe2x80x9cbxe2x80x9d and xe2x80x9ccxe2x80x9d.
FIGS. 6A-6G show the shapes of the iris aperture xe2x80x9cqxe2x80x9d and the states of the covering of the iris aperture xe2x80x9cqxe2x80x9d by the ND filter xe2x80x9cjxe2x80x9d, namely the states of the ND filter being inserted in the iris aperture xe2x80x9cqxe2x80x9d when the iris aperture xe2x80x9cqxe2x80x9d is gradually narrowed from an opened iris aperture state shown in FIG. 6A to a small iris aperture state shown in FIG. 6G by moving the iris blades xe2x80x9cbxe2x80x9d and xe2x80x9ccxe2x80x9d in the exposure controlling mechanism xe2x80x9caxe2x80x9d.
Incidentally, the exposure controlling mechanism xe2x80x9caxe2x80x9d has a problem that the not-covered portion xe2x80x9crxe2x80x9d formed at the time when the ND filter xe2x80x9cjxe2x80x9d does not cover the whole of the iris aperture xe2x80x9cqxe2x80x9d, as shown in FIG. 6E, at an intermediate process to the small iris aperture state, as shown in FIG. 6G, shows effects just like those in the small iris aperture state, such as degradation of the picture quality owing to diffraction and dust coming out owing to the increase of the depth of focus. Furthermore, there is another problem that light reflected from an image sensor or a surface of a seal glass hits the surface of the ND filter xe2x80x9cjxe2x80x9d on the image sensor side to come out in the screen by being reflected again at the surface of the ND filter xe2x80x9cjxe2x80x9d.
In view of the aforesaid problems, the present invention aims to prevent the degradation of the picture quality in the intermediate state in the process from the opened iris aperture state to the small iris aperture state and to decrease the reflected light coming out of the image sensor and the like.
For resolving the aforesaid problems, according to a first aspect of the invention, there is provided an imaging apparatus with an exposure controlling mechanism comprising a first iris blade to which a first ND filter having at least two levels of transmissivity is attached, a second iris blade to which no ND filter is attached; and a third iris blade to which a second ND filter having a single transmissivity is attached, in which the first to the third iris blades are made to differ respectively in amounts and phases of their displacements caused by the operation of a driving means.
Consequently, it becomes possible to control appropriately the shapes of the iris aperture and the insertion amounts of the ND filters into the iris aperture in accordance with various states of the iris aperture. And then, the degradation of picture quality at a specified diaphragm state, such as a small diaphragm aperture state, can be prevented.
Furthermore, according to a second aspect of the invention, the imaging apparatus of the first aspect is further characterized in that: the driving means for the first to the third iris blades includes a driving motor attached to the housing of the exposure controlling mechanism and an operation arm fixed to a rotation axis of the driving motor, the operation arm including three arm portions at a tip portion of each of which one connecting pin is projectingly fixed, respectively, the connecting pin being slidably engaged with an elongated link aperture of each of the first to the third iris blades, and the first to the third iris blades are made to differ respectively in amounts and phases of their displacements caused by a rotation of the driving motor owing to differences in the lengths of the three arm portions and the projection directions from the center of the driving motor of the operation arms.
Consequently, it becomes possible to control appropriately the shapes of the iris aperture and the insertion amounts of the ND filters into the iris aperture in accordance with various states of the iris aperture to the most suitable states.
Furthermore according to a third aspect of the invention, the imaging apparatus of the first aspect is further characterized in that: the first iris blade, the second iris blade and the third iris blade are arranged in order from the object side.
Consequently it becomes possible to prevent the iris aperture from becoming a small iris aperture state or becoming just like the small iris aperture state when the ND filter does not yet cover the whole of the iris aperture.
Furthermore according to a fourth aspect of the invention, the imaging apparatus of the first aspect is further characterized in that the first iris blade covers the iris aperture at a later time than the third iris blade.
Consequently, it becomes possible to decrease the reflected light coming out of the image sensor and the like.